Hydrogenation of aluminum using a supercritical fluid medium

ABSTRACT

An apparatus and a method for controllably converting aluminum into alane. In the system of the invention, a reaction between aluminum and hydrogen to form alane is performed at temperatures below 100° C. using a supercritical fluid such as CO 2  as a reaction medium, with the optional inclusion of a co-solvent, such as an ether, in the reaction vessel. Inert gas is used to exclude unwanted gases such as oxygen. The reaction of aluminum and hydrogen has been observed to proceed at approximately 60° C. using Me 2 O as an added solvent in CO 2  at supercritical pressures.

CROSS-REFERENCE TO RELATED APPLICATIONS

Application Ser. No. 13/053,117 is a continuation of and claims priorityand the benefit of U.S. patent application Ser. No. 11/951,588, filedDec. 6, 2007, issued as U.S. Pat. No. 7,931,887 on May 31, 2011, whichapplication claimed the priority to and benefit of U.S. provisionalpatent application Ser. No. 60/873,105, filed Dec. 6, 2006, whichapplication is incorporated herein by reference.

FIELD OF THE INVENTION

The invention relates to hydrogenation in general and particularly to asystem and method that employs a supercritical fluid medium tohydrogenate a metal.

BACKGROUND OF THE INVENTION

Hydrogen storage materials or media (HSMs) are a class of chemicalscontaining hydrogen in a chemically or physically bound form. They havewide potential utility in the areas of transportation, materialsmanufacture and processing and laboratory research. There is particularcurrent interest in HSMs for the first application: vehicles powered byfuel cells or internal combustion engines for use in a ‘hydrogeneconomy’ will require an on-board source of hydrogen fuel, and hydrogenis very difficult to store either as a gas or as a cooled liquid toprovide sufficient distance between refills.

Despite optimism over the last three decades, a hydrogen economy remainsa utopian vision. The US Department of Energy (DOE) Basic Science grouppublished a landscape report in 2003 summarizing the fundamentalscientific challenges that must be met before a hydrogen economy becomesviable. The report identifies the following desiderata for a viable HSM:

-   -   1. High hydrogen storage capacity (min 6.5 wt % H).    -   2. Low H₂ generation temperature (T_(dec) ideally around 60-120°        C.).    -   3. Favorable kinetics for H₂ adsorption/desorption.    -   4. Low cost.    -   5. Low toxicity and low hazards.

Alane, (AlH₃)_(x) is a polymeric network solid that contains 10.1 wt %hydrogen and undergoes dehydrogenation to simple, nontoxic Al powder. Itis an excellent candidate material to meet the long term DOE hydrogensystems goals. Since the time of filing of our earlier patentapplication entitled SYNTHESIS, RECHARGING AND PROCESSING OF HYDROGENSTORAGE MATERIALS USING SUPERCRITICAL FLUIDS (International Pat. App.PCT/CA2005/001908), alane has become a serious contender as an HSM forvehicular hydrogen storage. However, the enthalpy of dehydrogenation ofall known phases of alane indicate that direct rehydrogenation can beaccomplished only at extremely high pressures, and is therefore notviable as a large-scale technology. Thus the utilization of alane as apractically viable hydrogen storage material can only be realized ifalternative methods can developed for the hydrogenation of aluminum.Currently, there are no methods known to achieve this outcome, asidefrom the laborious, costly and wasteful route involving conversion of Alinto a corresponding halide or other derivative, followed by ametathesis reaction with a saline or complex hydride, as detailed inEquations 1 and 2.Al+3LiCl+1.5H₂→AlCl₃+3LiH (uptake of H₂)  Eq. 1AlCl₃+3LiH→Al+3LiCl+1.5H₂ (release of H₂)  Eq. 2

These reactions can be applied in a cycle, as illustrated in Scheme 1.It is believed that the hydrogen uptake reaction given by Equation 1converts the Al+3LiCl to AlCl₃+3LiH by way of the intermediatesAl+Cl₂+3Li+H₂ as shown on the left hand side of the cycle. It is furtherbelieved that the hydrogen release reaction given by Equation 2 convertsthe AlCl₃+3LiH to Al+3LiCl by way of the intermediates AlH₃+3LiCl asshown on the right hand side of the cycle.

Reports describing the use of alane as a chemical reagent appear in thepublic literature at least as early as 1947. U.S. Pat. No. 6,228,388issued May 8, 2001 to Petrie et al. describes various methods ofpreparing alane using metal hydrides as a source of hydrogen.

U.S. Pat. No. 6,536,485 issued Mar. 25, 2003 to O'Brien discloses ameans of room temperature packaging of hydrogen using a solvent such asethane or hexane: large amounts of H₂ gas can be dissolved in thesehydrocarbons when they are in a supercritical phase. O'Brien exploitsthe high miscibility of hydrogen with supercritical fluids, effectivelyusing the organic solvent as an HSM. At column 7, lines 41-42 the patentteaches that by using the systems and methods disclosed therein, “Thehigh weight of metal hydride type storing systems is also avoided.” Thisstatement appears to be teaching away from using metal hydrides for thestorage of hydrogen.

SUMMARY OF THE INVENTION

In one aspect, the invention relates to an apparatus for the conversionof aluminum to alane. The apparatus comprises a pressure vesselconfigured to contain a quantity of aluminum powder or alane. Theapparatus comprises sources of solvents (such as Me₂O, Et₂O and THF),gases or liquids (or more generally, fluids) capable of attaining asupercritical state (such as CO₂), and a source of hydrogen (such asgaseous H₂) in fluid communication with the pressure vessel. As needed,the apparatus comprises a source of inert gas, which can be useful inexcluding or removing room air from the pressure vessel and othercomponents of the reaction apparatus, so as to reduce the concentrationof reactive gases such as oxygen and water vapor found therein toacceptably low levels. The apparatus comprises one or more pumps asneeded to raise the pressure of fluids admitted into the pressure vesselto desired pressures. The apparatus comprises a heat source for heatingthe pressure vessel to a desired operating temperature and a cooler forcooling the pressure vessel to a desired temperature. The apparatuscomprises a stirrer for stirring the reaction medium. The apparatuscomprises a controller configured to control at least one of a fluidflow, a temperature and a pressure with the apparatus to fall within arespective one of a desired flow rate and direction, a desiredtemperature, and a desired pressure. In some embodiments, the aluminumcontains (or is doped with) a dopant, such as titanium. In oneembodiment, the controller is configured to control at least one of afluid flow, a temperature and a pressure within the apparatus is ageneral purpose programmable computer-based controller.

In another aspect, the invention relates to a method of generatingalane. The method comprises the steps of providing a pressure vessel;providing a controller configured to control at least one of a fluidflow, a temperature and a pressure within the apparatus to fall within arespective one of a desired flow rate and direction, a desiredtemperature, and a desired pressure; introducing aluminum metal into thepressure vessel; reducing the concentration of unwanted reactivematerials in the pressure vessel; introducing into the pressure vesselat least a substance capable of attaining a supercritical fluid state;introducing a source of hydrogen into the pressure vessel; raising atleast one of the temperature and the pressure within the pressure vesselto attain a supercritical fluid state, and reacting the aluminum withthe source of hydrogen to produce alane.

In one embodiment, the method further comprises the step of introducinga solvent into the pressure vessel. In some embodiments, the aluminummetal contains (or is doped with) a dopant (such as titanium). In someembodiments, the step of reducing the concentration of unwanted reactivematerials in the pressure vessel is performed using an inert gas. Insome embodiments, the substance capable of attaining a supercriticalfluid state is CO₂. In some embodiments, the source of hydrogen ishydrogen gas. In some embodiments, the solvent is an ether such as Me₂O,Et₂O, or tetrahydrofuran. In another embodiment, the method furthercomprises the steps of providing a molecule configured to form an adductwith alane; and after completion of the step of and reacting thealuminum with the source of hydrogen to produce alane, removing themolecule configured to form an adduct. The resulting product issubstantially pure alane. In some embodiments, the controller configuredto control at least one of a fluid flow, a temperature and a pressurewithin the apparatus is a general purpose programmable computer-basedcontroller. In one embodiment, the temperature is a temperature below100° C.

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent from the following descriptionand from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention can be better understood withreference to the drawings described below. The drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the drawings, likenumerals are used to indicate like parts throughout the various views.

FIG. 1 is a schematic diagram of an apparatus useful to carry out areaction to generate alane, according to the invention.

FIG. 2 is an image of a commercially available reactor for carrying outreactions using supercritical fluids.

FIGS. 3 and 4 are pressure-composition-temperature (PCT) graphs thatillustrate the progress of a dehydrogenation process for a specimen ofaluminum with titanium hydrogenated under conditions similar to thosedescribed hereinbelow.

FIG. 5 is a gas chromatograph (GC) plot that illustrates the release ofhydrogen from a sample of aluminum with titanium hydrogenated underconditions similar to those described hereinbelow, in which the lowercurve represents a control plot of the nitrogen carrier gas, and theupper curve represents the gas desorbed by heating the hydrogenatedsample of aluminum with titanium in the presence of the nitrogen carriergas.

FIG. 6 is an illustrative conceptual diagram of the 1:1 oxygen donorligand adduct AlH₃.Et₂O.

FIG. 7 is an illustrative conceptual diagram of the 1:2 oxygen donorligand adduct AlH₃.2THF.

FIG. 8 is an illustrative conceptual diagram of the 1:1 nitrogen donorligand adduct AlH₃.Me₃N.

FIG. 9 is an illustrative conceptual diagram of the 1:2 nitrogen donorligand adduct AlH₃.2TEDA.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the use of supercritical fluids (SCFs)as a medium to effect the hydrogenation of aluminum, thereby formingalane. Over the past decade, SCFs have developed from laboratorycuriosities to occupy an important role in synthetic chemistry andindustry. SCFs combine the most desirable properties of a liquid withthose of a gas: these include the ability to dissolve solids and totalmiscibility with permanent gases. For example, supercritical (sc) CO₂has found a wide range of applications in homogeneous catalysis,including such processes as hydrogenation, hydroformylation and olefinmetathesis. Heterogeneous catalyses carried out in scCO₂ includesFischer-Tropsch synthesis and hydrogenation. Furthermore, sCH₂O has alsofound wide utility in enhancing organic reactions.

Alane is a very attractive system for hydrogen storage, being a simplebinary hydride containing 10.1 wt % hydrogen with a theoretical Hdensity of 148 g/L, and possessing a higher volumetric hydrogen capacitythan liquid hydrogen. The material is marginally stable at roomtemperature, releasing H₂ between 60 and 140° C. Aluminum is cheap, safeand plentiful and is widely used in 21^(st) Century technologies. Alanethus clearly satisfies four of the five DOE criteria. According to theunderstanding prior to this invention, the major drawback is its lack ofreversibility: direct combination of Al and H₂ requires draconianpressures—in excess of 25 kbar. The thermodynamic properties of AlH₃vitiate conventional gas-solid synthesis: AlH₃ is thermochemically onthe cusp with respect to decomposition to Al and H₂ (the α-, β- andγ-phases of AlH₃ have ΔH_(dehyd) values of ca. +6, −4 and +1 kJ mol⁻¹,respectively). Thus, even at very high pressures of H₂, the modestthermal input needed to overcome the activation barrier will place thesystem thermodynamically in favor of the elements (i.e. to the left ofEq. 3).Al+1.5H₂⇄AlH₃  Eq. 3

SCFs have unique properties that allow us to overcome this antagonisticinterplay between the kinetic and thermodynamic properties of thesystem. The total miscibility of H₂ with a SCF is a distinct advantagein this respect, allowing effective concentrations of hydrogenequivalent to hundreds of bar to be attained easily and efficiently, andfavoring the thermodynamics of AlH₃ over the elements. In addition,conventional solvents may be added to the SCF medium to enhance thesolubility of reactants and/or products, allowing one to alter thekinetic and/or thermodynamic profile of the reaction (q.v.). This isparticularly important for a system like AlH₃ that is thermally fragile.Furthermore, the high diffusivity of permanent gases in SCF mediaencourages favorable kinetics to be established close to roomtemperature.

Examples of supercritical fluid systems and reaction conditions that canbe used to produce alane by direct hydrogenation of aluminum include,but are not limited to: CO₂ (75 bar), H₂ (30-50 bar) 50-60° C., 2-4 h;dimethyl ether (8 bar), H₂ (30-40 bar), 125° C., 2-4 h; ethane (65 bar),H₂ (30-40 bar), 90° C., 2-4 h; and ternary mixtures of Me₂O, CO₂ and H₂.

Preparative Example

FIG. 1 is a schematic diagram of the apparatus used to regenerate alanefrom a dehydrogenated sample of the material. In FIG. 1, there is showna high pressure reaction vessel 1, which is in fluid communication byway of piping and valves with a Me₂O cylinder 2, a CO₂ cylinder 3, a CO₂pump 4 and a H₂ cylinder 5. Customary symbols for valves are shown inthe lines connecting the various components of the apparatus.

A sample of alane prepared by conventional methods was doped with TiCl₃(2 mol %) in order to facilitate H₂ evolution and absorption, then thematerial was dehydrogenated, giving a light gray powder. A powder X-raydiffraction pattern of the resulting material showed only peaks arisingfrom Al. The material was then introduced into a 100 mL stainless-steelpressure reactor 1 under a blanket of inert gas. Examples of inert gasesthat are suitable for use in the systems and methods of the inventioninclude helium, argon and nitrogen. Nitrogen having negligible oxygencontent can be obtained as the boil-off gas from liquid nitrogen, or bygettering nitrogen over metal shavings heated to elevated temperatures(e.g., iron heated to 800° C.). See for example, J. B. Milstein and L.F. Saunders, “Gettering of Gases for High Purity Applications,” J.Crystal Growth 89, 124 (1988). A small amount of Me₂O was admitted fromtank 2 to vessel 1 as a vapor (50 psi) under its own head pressure.Liquid CO₂ (890 psi) was next admitted to vessel 1 from tank 3 with theaid of pump 4, and finally H₂, (500 psi was added from tank 5 to vessel1. The reaction mixture in 1 was then heated to 60° C., thereby forcingthe CO₂/H₂ mixture into a supercritical phase, and the contents werestirred at 150 rpm for 1 h. Preferably, a temperature below 100° C. isemployed. Suitable stirring apparatus can include any of a mechanicalstirrer and a magnetic stirrer. At this point, vessel 1 was cooled toroom temperature and all volatile material was removed by venting andpumping, for 1 h. Reaction vessel 1 was then disconnected from the othercomponents in FIG. 1, transported into an inert atmosphere glove box,and opened. revealing a gray powder, albeit slightly different in colorand appearance to the starting material.

In FIG. 1 features such as heating and cooling apparatus, vents to allowcomponents or reagents to be removed from the system and controllers tooperate the heating apparatus, the cooling apparatus and the valves arenot shown. Conventional pressure sensing equipment that provides anelectrical signal indicative of a pressure can be used to sense and tocontrol pressures in the various portions of the equipment. Electricallyor pneumatically operated valves can be used to control the timing andthe flow rates as gases and fluids are moved from one container toanother, or are held in a container, or are vented. Conventionalelectrical heaters and conventional fluid based (e.g., water) thermalexchange systems can be used to heat and cool the reaction vessel to themoderate temperatures required. Conventional thermal controllers, usingsensors such as thermocouples, and feedback circuits that sensetemperature and compare the temperature to a set point can be employed.In some embodiments, conventional general purpose programmable computerscan be used to implement the control functions for thermal control andfor pumping, mass flow, and pressure control.

In some cases, a person is permitted to control the valves and theoperation of the apparatus. It is anticipated that higher yields ofalane may be obtained. In particular, several factors could cause areduction of the amount of alane measured as compared to the amount ofalane produced in the process. First, the pressure of the system has tobe reduced to remove the alane, thereby reducing the partial pressure ofhydrogen available for equilibrium with the product, which might permitthe product to decompose to some unknown extent. In addition, thespecimen to be examined is removed from the vessel 1, and may be exposedto both oxygen and water vapor in the air ambient that is present duringthe analysis, even though the specimen is intended to be protected fromreactive environments during the analysis.

FIG. 2 is an image of a commercially available reactor for carrying outreactions using supercritical fluids. This reactor, and similar highpressure, compact laboratory reactors, are available from ParrInstrument Company, 211 Fifty Third Street, Moline, Ill. 61265-9984, orfrom several other sources. These reactors can be obtained withcontrollers that are used to monitor, control, datalog and archivevarious parameters, including temperature control, stirring speedcontrol, monitor pressure, log data, control gas and liquid feeds andhandle the product produced. In some instances a PC user interface isused to control one or more reactors.

FIGS. 3 and 4 are pressure-composition-temperature (PCT) graphs thatillustrate the progress of a dehydrogenation process for a specimen ofaluminum with titanium hydrogenated under conditions similar to thosedescribed with respect to FIG. 1.

FIG. 5 is a gas chromatograph (GC) plot that illustrates the release ofhydrogen from a sample of aluminum with titanium hydrogenated usingscCO₂ (˜70 bar)/H₂ (˜35 bar), for 20 hours at a temperature of 60° C.,in which the lower curve represents a control plot of the nitrogencarrier gas, and the upper curve represents the gas desorbed by heatingthe hydrogenated sample of aluminum with titanium in the presence of thenitrogen carrier gas.

Alternative Synthesis Method

In a second method we expect that a doped supercritical CO₂ reactionmedium can be used to prepare alane. We also expect that one can use acompletely different supercritical fluid, to create a betterthermodynamic environment.

It is expected that one can form an intermediate molecular alane adduct,L.AlH₃, whose enthalpy of complex formation (ΔHc) is more favorable thanthat of naked AlH₃, and which can then be heated to temperatures closeto ambient to remove the donor L and produce the desired polymeric(AlH₃)_(x) material. We believe that the likelihood of this procedureworking is high, as a similar two-stage process is employed to stabilizealane and then decomplex it in the so-called ‘organometallic route’ thatis currently the only method of making the material. It is expected thatthe donor molecule L, can be any one of a range of materials includingethers (such as Me₂O and Et₂O) and amines (such as Me₃N and Et₃N). Weexpect that either or both of the 1:1 and 2:1 L.AlH₃ complexes may serveas useful stabilized intermediates in the formation of alane. We expectthat the addition of molecular hydrogen transfer catalysts (e.g.Wilkinson's catalyst) to the SCF reaction mixture may also be effective,in addition to the solid-state catalysts (e.g. Ti) incorporated in theAl substrate.

As we have already explained, the marginal thermodynamic stability ofalane has thwarted its direct preparation from Al and H₂ according tothe reaction shown in Eq. 3 given above, except under conditions ofextreme temperature and pressure. We expect that the use of alternativeSCF media and mixtures with donor solvent or co-solvent capability,along with the use of hydrogen transfer catalysts, will allow thestabilizing of a molecular adduct of nL.AlH₃ intermediate (with n=1 orn=2), while subsequent removal of the donor L and transformation to thepolymeric binary hydride (Eqs. 4 and 5). It has already beendemonstrated that triethylenediamine (TEDA) can stabilize AlH₃sufficiently to permit direct reaction between Al and H₂ in conventionalhydrocarbon solvents to form polymeric AlH₃.TEDA. However, thestrongly-bound TEDA ligand is not removable from the AlH₃ in thisproduct, therefore rendering the adduct ineffective for preparation ofpure alane. See “The Direct Synthesis of Amine Alanes.” E. C. Ashby,Journal of the American Chemical Society, 1964, vol. 86, p. 1882. Seealso “The Direct and Reversible Synthesis of the AlH₃ Adduct ofTriethylenediamine (TEDA) Starting with Activated Al and Hydrogen,”James Joseph Reilly, Jason Graetz, James Wegryzn, Yusuf Celibi, JohnJohnson and Wei-Min Zhou, MRS Fall Meeting, Boston, 2007.

$\begin{matrix}{{Al}_{(s)} + {1.5\;{{H_{2{(g)}}\overset{L}{\longrightarrow}L} \cdot {Al}}\;{H_{3{(s)}}\underset{- L}{\overset{\Delta}{\longrightarrow}}( {{Al}\; H_{3}} )_{x{(s)}}}}} & {{Eq}.\mspace{14mu} 4} \\{{Al}_{(s)} + {1.5\;{H_{2{(g)}}\overset{2\; L}{\longrightarrow}2}\;{L \cdot {Al}}\;{H_{3{(s)}}\underset{{- 2}\; L}{\overset{\Delta}{\longrightarrow}}( {{Al}\; H_{3}} )_{x{(s)}}}}} & {{Eq}.\mspace{14mu} 5}\end{matrix}$

Examples of adducts that can be prepared (or that are believed to becapable of being prepared) include adducts using molecular oxygen donorligands such as dimethyl ether (Me₂O), diethyl ether (Et₂O), dioxane,ethylmethyl ether (MeOEt), tetrahydrofuuran (THF), and molecularnitrogen donor ligands such as pyridine, quinuclidine, trimethylamine(Me₃N), triethylamine (Et₃N), and triethylenediamine (TEDA).Representative DFT-calculated energies of complex formation (ΔHc) aregiven in Table I for oxygen donor ligands, and in Table II for nitrogendonor ligands, for the gas phase reactions described in Eqs. 6 and 7.AlH_(3(s))+L_((g))→AlH₃.L_((g))  Eq. 6AlH_(3(s))+2L_((g))→AlH₃.2L_((g))  Eq. 7

FIGS. 6 through 9 are diagrams of illustrative conceptual diagrams ofvarious one- and two-ligand adducts taken from the contents of Tables Iand II.

TABLE I 1:1 Complexes ΔHc (kJ/mol) 1:2 Complexes ΔHc (kJ/mol) AlH₃•Et₂O−71.52 AlH₃•2Et₂O ? AlH₃•MeOEt −77.68 AlH₃•2MeOEt −99.29 AlH₃•Me₂O−83.18 AlH₃•2Me₂O −113.69 AlH₃.Dioxane −84.41 AlH₃.2Dioxane −116.88AlH₃•THF −93.13 AlH₃•2THF −122.02

FIG. 6 is an illustrative conceptual diagram of the 1:1 oxygen donorligand adduct AlH₃.Et₂O.

FIG. 7 is an illustrative conceptual diagram of the 1:2 oxygen donorligand adduct AlH₃.THF.

TABLE II ΔHc 1:1 Complexes ΔHc (kJ/mol) 1:2 Complexes (kJ/mol) AlH₃•Et₃N−89.02 AlH₃•2Et₃N ? AlH₃•Me₃N −108.15 AlH₃•2Me₃N −145.80 AlH₃.pyridine−109.24 AlH₃.2Pyridine −142.12 AlH₃.TEDA ? AlH₃.2TEDA −155.56AlH₃.Quinuclidine −118.45 AlH₃.2Quinuclidine −156.24

FIG. 8 is an illustrative conceptual diagram of the 1:1 nitrogen donorligand adduct AlH₃.Me₃N.

FIG. 9 is an illustrative conceptual diagram of the 1:2 nitrogen donorligand adduct AlH₃.2TEDA.

Various uses for alane material can be suggested, including hydrogenstorage, provision of hydrogen recovered from alane, and use of alanefuses in solid fuels for booster rockets.

General Purpose Programmable Computers

General purpose programmable computers useful for controllinginstrumentation, recording signals and analyzing signals or dataaccording to the present description can be any of a personal computer(PC), a microprocessor based computer, a portable computer, or othertype of processing device. The general purpose programmable computertypically comprises a central processing unit, a storage or memory unitthat can record and read information and programs using machine-readablestorage media, a communication terminal such as a wired communicationdevice or a wireless communication device, an output device such as adisplay terminal, and an input device such as a keyboard. The displayterminal can be a touch screen display, in which case it can function asboth a display device and an input device. Different and/or additionalinput devices can be present such as a pointing device, such as a mouseor a joystick, and different or additional output devices can be presentsuch as an enunciator, for example a speaker, a second display, or aprinter. The computer can run any one of a variety of operating systems,such as for example, any one of several versions of Windows, or ofMacOS, or of Unix, or of Linux.

In operation, a general purpose programmable computer is programmed withinstructions in the form of software or firmware. The instructionscontrol the operation of the general purpose programmable computer/Thegeneral purpose programmable computer can perform a variety ofmanipulations of data, such as mathematical operations (e.g.,calculations), logical operations (e.g., comparisons, or logicaldeductions following defined rules), and processing of textual orgraphical data (e.g., word processing, or image processing). Data can beprovided to the general purpose programmable computer as recorded dataor as real-time data. The result of any computation or processingoperation is recorded in a machine-readable medium or memory forimmediate use or for future use. For example, in micro-processor basedanalysis modules, data can be recorded in a register in amicroprocessor, in a cache memory in the microprocessor, in local memorysuch as semiconductor memory (e.g., SRAM, DRAM, ROM, EPROM), magneticmemory (e.g., floppy disc or hard disc) and/or optical memory (e.g.,CD-ROM, DVD, HD-DVD), or in a remote memory such as a central database.Future use of data recorded in a machine-readable medium can includedisplaying, printing, or otherwise communicating the data to a user,using the data in a further calculation or manipulation, orcommunicating the data to another computer or computer-based device.

Machine-readable storage media that can be used in the invention includeelectronic, magnetic and/or optical storage media, such as magneticfloppy disks and hard disks; a DVD drive, a CD drive that in someembodiments can employ DVD disks, any of CD-ROM disks (i.e., read-onlyoptical storage disks), CD-R disks (i.e., write-once, read-many opticalstorage disks), and CD-RW disks (i.e., rewriteable optical storagedisks); and electronic storage media, such as RAM, ROM, EPROM, CompactFlash cards, PCMCIA cards, or alternatively SD or SDIO memory; and theelectronic components (e.g., floppy disk drive, DVD drive, CD/CD-R/CD-RWdrive, or Compact Flash/PCMCIA/SD adapter) that accommodate and readfrom and/or write to the storage media. As is known to those of skill inthe machine-readable storage media arts, new media and formats for datastorage are continually being devised, and any convenient, commerciallyavailable storage medium and corresponding read/write device that maybecome available in the future is likely to be appropriate for use,especially if it provides any of a greater storage capacity, a higheraccess speed, a smaller size, and a lower cost per bit of storedinformation. Well known older machine-readable media are also availablefor use under certain conditions, such as punched paper tape or cards,magnetic recording on tape or wire, optical or magnetic reading ofprinted characters (e.g., OCR and magnetically encoded symbols) andmachine-readable symbols such as one and two dimensional bar codes.

While the present invention has been particularly shown and describedwith reference to the structure and methods disclosed herein and asillustrated in the drawings, it is not confined to the details set forthand this invention is intended to cover any modifications and changes asmay come within the scope and spirit of the following claims.

What is claimed is:
 1. A method of generating alane, comprising thesteps of: providing a pressure vessel; providing a controller configuredto control at least one of a fluid flow, a temperature and a pressurewithin the apparatus to fall within a respective one of a desired flowrate and direction, a desired temperature, and a desired pressure;introducing aluminum metal into the pressure vessel; reducing theconcentration of unwanted reactive materials in the pressure vessel;introducing into the pressure vessel a fluid capable of attaining asupercritical fluid state; introducing a source of hydrogen into thepressure vessel; raising at least one of the temperature and thepressure within the pressure vessel to attain a supercritical fluidstate; and reacting the aluminum with the source of hydrogen to producealane.
 2. The method according to claim 1, further comprising the stepof introducing a solvent or co-solvent into the pressure vessel.
 3. Themethod according to claim 2, wherein said solvent is an ether.
 4. Themethod according to claim 3, wherein said ether is a selected one ofMe₂O, Et₂O, and tetrahydrofuran.
 5. The method according to claim 1,wherein said step of reducing the concentration of unwanted reactivematerials in the pressure vessel is performed using an inert gas.
 6. Themethod according to claim 5, wherein said inert gas is a selected one ofhelium and argon.
 7. The method according to claim 5, wherein said inertgas is nitrogen.
 8. The method according to claim 1, wherein said fluidcapable of attaining a supercritical fluid state is CO₂.
 9. The methodaccording to claim 1, wherein said source of hydrogen is hydrogen gas.10. The method of claim 1, wherein said controller configured to controlat least one of a fluid flow, a temperature and a pressure within theapparatus is a general purpose programmable computer-based controller.11. The method of claim 1, wherein said temperature is a temperaturebelow 100° C.